Iron corrosion in leather boot

Andrew Hawley <manticle<-at->hotmail<.>com> writes

>I am working out some treatment options for a leather boot found
>under the site of a small heritage centre during construction.  The
>centre would like to display it (aesthetically 'as is' so no major
>restoration or repair necessary) early next year as part of a
>display on the history of the centre.  However the sole of the boot,
>particularly near the heel and toe is significantly deteriorated and
>has the appearance of advanced iron corrosion/rust.  There are what
>looks like old nails or tacks and it is possible that the boot was a
>steel reinforced construction worker's boot. ...

Archaeological leather often is excavated wet or damp, and ideally
is not dried out until treated. Presumably the boot has already been
dried, which makes treatment more difficult. I wouldn't recommend
the alkaline treatments such as sodium hydroxide or sodium
carbonate. These treatments require prolonged soaking and the alkali
will damage the leather.

The first thing to do is to pass a magnet over the corroded areas.
If there is no magnetic pull, then the iron is all corroded and no
iron treatment is necessary. No further corrosion can happen.

If metallic iron is present then you may have to treat it. If the
boot can be rehydrated and washed that would probably be the best
option, but might not be possible. You would have to test.
Archaeological leather is usually quite robust to wet treatments.
Freeze drying is the best way to dry after wet treatment. Any
crumbling areas could be consolidated with B72 or another
consolidant. If you don't want the boot to look any different,
that's all you would do. If the wet treatment is a no go, then the
best option is to control the environment, reduce the humidity as
much as you can, and keep it at a stable level. Anoxic display is
another option, but expensive, and a continuous expense.

If you were being more interventive, then you would reshape while
wet, mechanically clean off any concretion (before, during and after
wet treatment), and possibly coat the metal areas with tannic acid
(after drying).

Valerie Tomlinson
Conservator
Auckland War Memorial Museum
Tamaki Paenga Hira
The Domain
Private Bag 92018
Victoria Street West
Auckland 1142
New Zealand
+64 9 306 7070 ext 7304


                                  ***
                  Conservation DistList Instance 27:26
                 Distributed: Monday, December 16, 2013
                       Message Id: cdl-27-26-005
                                  ***